ok here goes, I have a 96 Kodiak ymf400 4wd. The quad used to run great just smoked like a freight train so I did a top end rebuild and rings. fixed my smoking problem. while it was out I went ahead and re-cleaned the aftermarket carb on it(which always ran fine) but now It pops and back fires any time above 1/2 throttle and while decelerating. it will push through the backfire and keep going but its pretty bad. I pulled the choke and did a pull which tells me it is too lean so I've been adjusting the needle but 1 and 2 clicks richer only makes it run worse. which makes no sense to me. how can it be to lean but richening it makes it worse? it has a new plug, the cam timing and valve clearances are spot on. what could it be. the only potential issue I have found is when I plug the intake with my hand it doesn't shut the bike off.. should it? also when I had the had off I cleaned the valve ports by hand because they were terribly corroded. ive adjusted the carb every which way and nothing seems to help. maybe I need a bigger main since the air flow is so much better but I really don't know and jets are hard to come by and not something I want to guess at. any help is appreciated, thanks in advance guys.

 

I posted this in the wrong section, cant figure out how to delete it

 

Stock main jet shows a 105,a 45 pilot jet.Items #13,15 Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse
If you can't richen the needle or the fuel screw(mainly for idle) enough to compensate for the lean running, then I'd jump a couple sizes up,say to a 110,112.5 for example. Plenty of Mikuni and Keihin carb jets here.Just tial and error on jetting. Main thing is to check the spark plug. Needs to be a tan to medium brown color after jetting changes.YAMAHA KODIAK YFM400 main pilot slow jets kit

 

I will definitely try that if its a possibility but if you don't mind my asking how can it need a bigger main jet to run right if it's completely stock? and it seems no matter where I move the needle jet it makes no difference at all

 

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If pulling the choke makes it run better,it's either running lean(jetting,carb passages/jets stopped up) or you possibly may have an air leak at the intake manifold,etc.

 

OK cool. I think that has to be it because I just took the whole carb out. Re cleaned it and adjusted the needle Richer and its the same thing. If I cover the intake partially it runs perfect so its gotta be to lean. Possibly on top of an intake leak because I rtv'd a couple questionable spots on the intake from the carb to the head and now it'll shut down when I cover the intake so I'm sure it had some leaks but now its a little better. I'm going to buy some jets and a new intake and hope for the best.. THANK YOU

 

Just take a little contact cleaner,wd40,etc and spray around the intake manifold and base gaskets,etc and see if the engine rpms change.

 

I sprayed the heck out of it and there's no change but then again its hard to tell because now its idling strange. It will idle up until I "pop" the throttle then it'll come down. But as far as I can tell no difference when sprayed(with carb cleaner)